The Transgenic and Chimeric Mouse Core Facility of the University of Pennsylvania has been in operation since February 1992 under the co-direction of Drs. Nancy Cooke and Stephen Liebhaber, and under the day-to-day technical coordination of Dr. Jean Richa. The Core was established with financial contributions by the School of Medicine in 1989. During the last competitive DERC renewal cycle in 1996 the Core received an evaluation of outstanding merit. Over the subsequent 5 years of service the Core has generated a wide range of transgenic and gene-targeted mouse lines that have proven to be powerful tools for the study of the molecular biology and physiology of Type I and Type II diabetes and other disorders of endocrinology and metabolism. The Core laboratory is located in a pathogen-free microbiologic barrier facility in the basement of the Clinical Research Building. A primary function of the Transgenic and Chimeric Mouse Facility has been and will continue to be to provide a centralized laboratory that will generate infection-free, transgenic founder or chimeric strains of mice carrying transgenes or gene mutations of specific interest to individual projects in the Diabetes and Endocrinology Research Center. The centralization of these technically demanding procedures in the Core laboratory results in enhanced efficiency and cost reduction for each project. During the current project period, the Transgenic and Chimeric Mouse Facility has grown significantly in service offerings and its facilities have been improved and expanded. A major increase in the size and throughput potential of the Core is now in progress to double service capacity in line with increasing demand for service. The Core will continue to maintain the highest level of quality service and will continue to acquire new techniques and expertise to maintain services at a state-of-the-art level.